1. Field of the Invention
The present invention is in the field of anilox rollers and relates more particularly to a device and method for measuring the volumetric capacity of the cells of anilox rolls and to an inexpensive disposable device for rapidly effecting such measurement.
2. The Prior Art
Anilox rolls (such term to include fluid metering or fluid transfer rollers) are employed in various industries, and particularly the printing industry for the purpose of transmitting metered quantities of a fluid, such as printing ink from a fountain or like fluid supply to a surface such as the surface of a printing cylinder. Such anilox rolls are comprised of cylinders, the surface of which is formed with a multiplicity of regularly spaced indentations or cells of any of a variety of geometric shapes and concentrations in accordance with the end use of the roll.
In application, the surface of the roll is contacted either directly with liquid contained in a fountain or with a roll which in turn is immersed partially in the fountain, such that the surface of the anilox roll is progressively coated with the fluid to be metered. The surface of the coated roll is thereafter scanned by a doctor blade, squeegee or like expedient which functions to remove excess fluid from the land areas between the cells, whereby the fluid carried by the anilox roll is encompassed entirely within the cells.
The surface of the roll, after doctoring, is thereafter applied against the roll or surface to which the fluid is to be transferred, illustratively the print cylinder of a printing press, whereby precisely measured quantities of fluid are transferred from the cells to the contacting surface.
The surface of the anilox roll may be formed of metal or more recently of ceramic.
Since the quantity of fluid transferred is, in large measure a function of the volume of the cells, it will be readily appreciated that with use and consequent wear of the cylinder surface, the volumetric capacity of the cells will progressively decrease.
While the volumetric decrease of cell capacity can, to a degree, be compensated by varying the characteristics of the ink employed, it is important for the user to be able to measure the cell capacities from time to time after periods of use.
Volumetric capacity of cells is conventionally expressed in terms of billion cubic microns (BCM) per square inch and in accordance with the intended end use may vary from as low as about 1 BCM per square inch to 300 or more BCM per square inch.
One known method for measuring the volumetric capacity of the cells of an anilox roll is discussed in U.S. Pat. No. 4,628,728 of Dec. 16, 1986.
In accordance with such method, a precisely metered quantity of fluid is deposited on a surface area of the roll to be measured. Thereafter a sheet of graph paper is superposed over the ink deposit and the sheet is doctored or roller pressed so as to follow the surface contours of the land areas of the roller and spread the deposited liquid. As a result, the fluid fills the cells of a certain surface area of the roller.
Upon removal of the graph paper an ink blot will remain on the graph paper, the area of which is inversely proportional to the cell volume, i.e. the lower the cell volume the wider spread the blot and vice versa.
In order to derive an empirical value in BCM, the user must first establish the precise area of the blot. In order to determine the blot area, it is necessary for the user to count the number of squares of the graph paper which are filled and partially filled, a procedure which is time consuming and somewhat inaccurate in that counting of partially filled squares (whether less than or more than half filled) involves subjective decisions.
In addition, the use of a pipette to transfer fluid itself involves a source of inaccuracy.
After determining the area of the blot, the user must mathematically compute the volume in BCM in accordance with a formula as set forth in the noted patent.
In order to simplify the area measurement required by the aforesaid patent, there is provided, in accordance with U.S. Pat. No. 4,800,287 of Jan. 24, 1989 an electronic area measuring device wherein the area is determined in accordance with stored pixel data.
Devices in accordance with the '287 patent are costly, being priced in the area of many thousands of dollars, and accordingly it is impracticable for any but the largest users of anilox rollers to own such apparatus.